Chemical and biological characterization of sapinopyridione, a phytotoxic 3,3,6-trisubstituted-2,4-pyridione produced by Sphaeropsis sapinea, a toxigenic pathogen of native and exotic conifers, and its derivatives

A phytotoxic trisubstituted 2,4-pyridione, named sapinopyridione (I), was isolated from the culture filtrates of Sphaeropsis sapinea, a fungal pathogen of conifers occurring world-wide. Three strains were isolated from two cypress species. Strain D-55 isolated from Cupressus sempervirens resulted high producer of sapinopyridione (12.3 mg l-1), whereas strain D-54 isolated from the same cypress species was low producer (1.1 mg l-1); strain D-50 isolated from C. macrocarpa was intermediate producer (5.4 mg l-1). Sapinopyridione was characterized by spectroscopic and chem. methods, as the 6-methyl-2-(2-methyl-1-oxobutyl)-1-oxa-5-azaspiro[2.5]oct-6-ene-4,8-dione. The structure was supported by the prepn. of three key derivs., whose phytotoxic and antimycotic activities were also tested on host plants and on three Seiridium species, virulent fungal agents of cypress canker disease. Some structure-activity relationships were identified for both phytotoxicity and antifungal activities. These activities appear related to the presence of both pyridione and oxiran rings. Also the carbonyl group of the side chain seems to play a role into impart activity.